United States patent document 2011/0049652 A1 discusses a vertically integrated component of this type and a method for its manufacture. The known method provides that the starting substrate for the MEMS component is bonded to an ASIC substrate which is already processed and optionally also structured. Only then is a micromechanical structure produced in the MEMS substrate. A cap wafer is independently structured and prepared for the mounting above the micromechanical structure of the MEMS substrate and on the ASIC. After the MEMS substrate is structured, the cap wafer processed in this way is bonded to the ASIC substrate, so that the micromechanical structure is hermetically sealed in a cavern between the ASIC substrate and the cap wafer.
The known method allows cost-effective mass production of robust components having a micromechanical sensor or actuator function, and an evaluation or control circuit, since in this case not only are the individual components (ASIC component, MEMS component, and cap) produced in the wafer composite, but in addition their mounting on a sensor component or actuator component on the wafer plane is achieved. The MEMS functions and the ASIC functions may be tested on the wafer plane, and the individual components may even be compared on the wafer plane. The stacked configuration of the known components likewise contributes to a reduction in the manufacturing costs, since these components require only a comparatively small mounting surface in the second-level mounting.
The cap wafer already protects the micromechanical structures of the individual MEMS components from soiling and damage during the further processing of the wafer stack. Thus, for example, particles which arise during sawing of the wafer stack for separation of the components are not able to settle in the micromechanical structures of the MEMS substrate. In a molding process for packaging the components, the cap prevents the molding compound from penetrating into the micromechanical structure of the MEMS component and impairing its functionality. In addition, the risk of component damage during the second-level mounting is significantly reduced by the cap, since the sensitive micromechanical structure of the component is not freely accessible, but, rather, is enclosed in the cavern between the cap and the ASIC component.
As a result of this encapsulation, the micromechanical structure of the MEMS component protects against soiling, moisture, and other environmental influences which impair functioning, even after manufacture and mounting of the component at the point of use.
With the aid of the cap, in addition a certain damping behavior which is coordinated with the type of component or its function may be specified and ensured over the service life of the component. For acceleration sensors, a critical damping behavior, for example, is usually sought, while yaw rate sensors require a high quality. For this purpose, the cavern internal pressure should be as low as possible.
This requirement may be met only with a sufficiently large cavern volume, since a certain degree of outgassing always occurs at the cavern wall and the MEMS surfaces within the cavern. Consequently, the distance between the cap cover and the micromechanical structure or the ASIC component must be appropriately large.
For capacitively operating MEMS components, there is another reason to select the distance between the cap cover and the micromechanical structure to be not too small, namely, the electrostatic influences of the cap on the electrical fields at the capacitors of the MEMS component. If the cap is situated too close to the micromechanical structure, the electrical fields of the capacitors of the MEMS component are deformed, which in the case of a sensor element affects the measuring signal, and in the case of an actuator element affects the control.
For both of the above-mentioned functions, i.e., protecting the micromechanical structure against soiling and adverse environmental influences, and ensuring a defined damping behavior of the micromechanical structure of the MEMS component, the cap may also still function as overload protection for the deflectable structural element of the MEMS component. Very high stresses on the micromechanical structure may occur, for example, if the component is dropped or subjected to impacts during the mounting process. This may result in excessive deflection of individual structural elements from the component plane, and may even result in catching and breaking within the micromechanical structure. Such damage may be avoided with the aid of an overload protection which limits the deflection of the micromechanical structure from the component plane.